The present invention relates to a thermal analysis apparatus and a thermal analysis method to reveal how a physical property of a material varies with temperature. Particularly, the invention relates to a novel improvement for suppressing uncertainty in temperature measurement which inevitably occurs upon measuring a large-sized sample.
Thermal analysis is an approach used to analyze a change in a physical or chemical property of a material as a function of temperature, and based on simultaneous measurements of material temperature and physical property. Various thermal analytic methods have so far been developed depending on the kind of physical property to be measured, typical ones of which, if rearranged in relation between technique and physical property, are as follows.
Differential scanning calorimetry (DSC): differential heat flow
Thermogravimetric measurement (TG): weight
Thermomechanical analysis (TMA): dimension
Dynamic thermomechanical analysis (DMA): modulus of elasticity
Dielectric thermal analysis (DETA): dielectric constant
In these thermal analysis methods, sample temperatures have been measured by temperature sensors such as thermocouples and resistor thermometers arranged in the vicinity of samples.
In order to accurately measure the temperature of a sample, it is desired to avoid a temperature distribution in the sample. Due to this, it is a general practice in thermal analysis to conduct measurement by decreasing the amount of a sample as much as possible so long as the sensitivity of physical property measurement does not become insufficient. The technique of reducing sample amount is effective for many applications where ingredient distribution in a sample does not cause problems. Particularly, significant effects are available in DSC and TG. Further, in DSC and TG, temperature distribution is suppressed by accommodating a sample in a vessel formed of aluminum or the like as a good heat conductive material. Furthermore, a temperature sensor such as a thermocouple contacted with a sample vessel is used for temperature detection.
That is, it is possible in DSC and TG to satisfy comparatively easily three elements of sample amount decrease, homogeneous sample heating by a good heat conductive vessel, and contact between a sample and a temperature sensor. As a result, they greatly contribute to accurate measurement of sample temperature.
However, in the case of TMA or DMA, it is difficult to satisfy, such conditions as sample amount decrease and homogeneous heating due to a vessel, of the three conditions to be easily satisfied by DSC and TG. Thus, situations become severe to accurately measure sample temperature.
DSC and TG in nature are not concerned with sample shape whereas in TMA information about sample length is important. For example, in expansion coefficient measurement as one of the important applications for TMA, it becomes requisite to know concretely a sample initial length. DMA deals with a modulus of elasticity as a ratio of stress to strain caused in a sample. Then, in order to accurately determine a modulus of elasticity, it is essential to accurately know at least a sample three dimensional shape.
That is, in TMA and DMA the sample tends to increase in diameter and hence a technique cannot be used to improve measurement accuracy of sample temperature, such as sample amount decrease and homogeneous heating.
Further, because of the restriction that no effect should be caused to reduce high accuracy dimensional measurement or strain measurement, it is difficult to put a temperature sensor in contact with a sample center. Moreover, even if measurement could be conducted with a temperature sensor contacted with a sample, a problem arises due to a temperature distribution caused by diameter increase such that it is uncertain whether a measured sample temperature correctly represents a sample overall temperature.
As stated above, in TMA and DMA the sample tends to increase in diameter. Due to this, there has arisen a problem that sample temperature measurement is inaccurate.
In particular, when precisely determining the coefficient of thermal expansion, the amount of sample expansion can be determined comparatively accurately. However, it has been a bottleneck to precisely measure a sample temperature.
The present invention has been developed in order to effectively solve the above problems. In a thermal analytic technique such as TMA or DMA in which an increase in diameter of a sample is inevitable, first a reference substance having a known temperature dependency of a physical property value and a sample to be measured are measured in physical property at the same time within the same furnace or under the same heating conditions. Next, in place of measuring a sample temperature using a temperature sensor such as a thermocouple arranged in the vicinity of the sample, a physical property change signal obtained by measuring a physical property value of the reference substance is converted into a temperature change signal. At this time, if the reference substance and the sample were separately measured in physical property change under the same heating conditions, the physical change of the reference substance with respect to an elapsing time from a measurement start is converted into a temperature change in the sample with respect to the elapsing time. Hereinafter, the analysis is proceeded similarly to usual thermal analysis.
In this process, the physical property change of the reference substance is used as a temperature sensor. Even in a large diameter sample, reduction in temperature measurement accuracy does not occur as a result of an arrangement or contactability of a temperature sensor.